A man who used a hammer to kill an Oak Grove woman pleaded guilty to murder and will be sentenced to a minimum of 25 years in prison.

Daniel James Seale, 27, killed Michelle Leigh Walker, whose body was found July 8 in her apartment. Seale immediately confessed to the crime, according to a detective who interviewed him.

Seale accepted a plea agreement this week and will be sentenced Dec. 19.

It is not clear why Seale killed Walker. That key detail should be disclosed when he is sentenced.

Walker's mother, Darlene Ann "Dolly" Spencer of Oak Grove, said her daughter met Seale when he was doing small handyman-type jobs for a neighbor.

In an unrelated case, Seale is scheduled to plead guilty Wednesday in Washington County to first-degree sexual abuse. The case involves a 2007 incident involving a relative, who was 13 at the time, said Clackamas County prosecutor Bryan Brock. As part of his plea agreement, Seale will receive six years and three months in prison. The murder and sex crime sentences are concurrent.

Seale has an extensive criminal history and was ordered to register as a sex offender in January, when he was convicted in Benton County of encouraging child sexual abuse in a pornography case.

In 2003, Seale was convicted of first-degree burglary and first-degree theft in Clackamas County. He also was convicted of third-degree theft in Multnomah County the same year.